The hematopoietic transcription factor PU.1 represses gelatinase A transcription in glomerular mesangial cells

The matrix metalloproteinase gelatinase A plays a key role in the evolution of glomerular injury and is a major contributing factor to the development of glomerulosclerosis, Prior studies have focused on a potent cis-acting e nhancer element located in the near 5'-flanking region of the rat and human gelatinase A genes (Harendza, S., Pollock, A. S., Mertens, P. R., and Love tt, D. H. (1995) J. Biol. Chem. 270, 18286-18796; Mertens, P. R., Alfonso-J aume, M. A., Steinmann, K., and Lovett, D. H. (1999) J. Am. Soc. Nephrol. 1 0, 2480-2487). Given the combinatorial nature of transcriptional regulation , we examined additional regions of the 5'-flanking region of the rat gelat inase A gene to identify further regulatory elements. In this study the ide ntification of a silencing element located between -1903 and -1847 base pai rs of the 5'-flanking region of the rat gelatinase A gene is reported. Sequ ence analysis, electrophoretic mobility studies, and transfection experimen ts demonstrate that a specific binding sequence for the hematopoietic trans cription factor PU.1 is present within the silencing sequence. PU.1 activit y is absolutely required for the expression of silencing activity within th e context of transfected glomerular mesangial cells. Western blots identify the PU.1 protein within nuclear extracts of mesangial cells, and cotransfe ction with a PU.1 expression vector directly augments silencing activity. T hese studies underscore the complex patterns of gelatinase A transcriptiona l regulation and also strongly suggest that glomerular mesangial cells are ultimately derived from bone marrow cells.